1. Never underestimate the power of minions. Seriously. They can take entire towers all by themselves, and the player that knows how minions work can win trades and the lane any time over the player that doesn't.
2. If you aren't already, practice getting the killing blow on minions, since it's only the killing blow which gives you gold. If you ever spectate a pro game, make notice of how much gold they get from getting the last hit on minions.
3. Watch Champion Spotlights to familiarize yourself with champions you aren't familiar with. Watch livestreams of pro players and make note of all of the small things they do, like kiting and harassing and dancing along the melee line and lasthitting and warding; you can also do the same by spectating pro games (make sure you're watching Ranked games!).
4. When trying new champions, don't think about whether you like the champion so much as whether you understand the champion. That sounds bad, but it really is true. At your level of play, winning games ends up making the game more fun, and you need the extra IP from wins more than a level 30 does. Once your level 30 you have more tools which let you make any champion work, but right now focus on experimenting and seeing what your playstyle is, and what you understand the most about the game.
5. Learn what all the items do, how they interact with one another, how they interact with certain champions, etc. Doing that will make you a much more dynamic player, and will always give you the upper hand over someone who doesn't understand items as much. What you do with your gold matters much more than how much gold you have, although the latter is very important.
6. Might not be as important at level 7, but wards win games. Just know that. It's much easier to escape from a 4 man gank if you can see the enemy before they reach your lane.

...That's all I got right now. Besides, I'm reaching my character limit.

You ever seen an anonymous comment so helpful? He pretty much nailed it man. That's all the game is. Positioning is key too, especially if you are playing ADC... Everything else is learning from just playing the game, ie jungling, initiating, etc...